Inhibition of N-butyl-N-(4-hydroxybutyl)nitrosamine-induced rat urinary bladder carcinogenesis by alpha-difluoromethylornithine.

The effect of oral administration of alpha-difluoromethylornithine (DFMO), an irreversible ornithine decarboxylase inhibitor, on N-butyl-N-(4-hydroxybutyl)nitrosamine (BHBN)-induced rat urinary bladder carcinogenesis was investigated. Four-wk-old male Fischer 344 rats, 30-38 per group, were divided into 3 groups; each group was divided into 3 subgroups. In Group A, 6-wk treatment with 0.05% BHBN in drinking water was followed by either 0.5% (A1), 0.2% (A2), or 0% (A3) DFMO in drinking water for 34 wk. In Group B, coadministration in drinking water of 0.01% BHBN and either 0.5% (B1), 0.2% (B2), or 0% (B3) DFMO was continued for 30 wk. Group C consisted of animals receiving 0.5%, 0.2%, or 0% DFMO in drinking water for 34 wk without prior or cocarcinogen treatment. Bladder tumorigenesis was clearly inhibited by DFMO; tumor incidence was 14 of 37 (38%) in A1, 16 of 38 (42%) in A2, and 31 of 35 (89%) in A3, and 7 of 35 (20%) in B1, 14 of 35 (40%) in B2, and 28 of 35 (80%) in B3 (P less than 0.01, DFMO groups as compared to the respective control A3 or B3). The average tumor volume was strikingly reduced in Group A rats given DFMO (3.0 mm3 in A1, 5.0 in A2, and 38.6 in A3). Significant suppression of tumor multiplicity (number of tumors/tumor-bearing bladder) was observed in DFMO-treated subgroups in Group B (1.1 in B1, 1.3 in B2, and 1.8 in B3). In both Groups A and B, however, DFMO failed to suppress hyperplastic changes (simple hyperplasia) or preneoplastic lesions (nodulopapillary hyperplasia). Systematic examination of all pertinent organs excluding the brain showed no adverse effects attributable to DFMO treatment except for decrease in body weight (less than 7%), which was consistently observed in the groups receiving 0.5% DFMO, and reduction in the combined weight of the prostate and seminal vesicles (less than 20%), which was noted in Group B in which exposure to DFMO was started at a younger age. These results indicate that oral administration of DFMO is quite effective in suppressing (or retarding) BHBN-induced carcinogenesis with minimal untoward effects and confirm the similar inhibitory effects demonstrated earlier with the heterotopically transplanted rat urinary bladder system.